Generally, isophthalic acid is produced through liquid-phase oxidation reaction of a m-phenylene compound (e.g., m-xylene) in acetic acid serving as a solvent in the presence of a catalyst (e.g., cobalt or manganese), or in the presence of a catalyst together with a promoter (e.g., a bromine compound or acetaldehyde). A slurry containing crude isophthalic acid produced through such liquid-phase oxidation reaction is generally subjected to crystallization at ambient pressure and lowered temperature, followed by solid-liquid separation.
A mother liquor recovered through the solid-liquid separation contains catalyst-derived useful catalyst components such as heavy metal ions and bromide ions, and an industrial process requires recycling of these catalyst components for reduction of production cost. In the most convenient recycling method, the mother liquor is returned, as it is, to and reused in the reaction system. However, as has been known, since the mother liquor contains, for example, various organic impurities by-produced through liquid-phase oxidation reaction, and inorganic impurities derived from corrosion of an employed apparatus, when the mother liquor is reused as it is in the reaction system, the concentration of these impurities is gradually increased in the reaction system, and an increase in impurity concentration beyond a predetermined level adversely affects liquid-phase oxidation reaction. For example, in the case of production of isophthalic acid, the mother liquor is generally returned to the reaction system in a proportion of 60 to 90%, and the remaining portion (10 to 40%) of the mother liquor (i.e., a portion of the mother liquor which is not reused in the reaction system) is fed to a step of recovering acetic acid serving as a solvent. In view of the foregoing, various methods have been proposed for recovering catalyst components from the mother liquor fed to such an acetic acid recovery step, and reusing the catalyst components.
For example, such known methods include a method in which water and an alkali metal carbonate salt are added to a residue obtained through recovery of a solvent from a mother liquor, to thereby cause a catalyst component in the form of carbonate salt to precipitate, and the catalyst component is dissolved in a predetermined amount of acetic acid serving as a solvent, and reused for reaction (see Patent Document 1); and a method in which oxalic acid and an alkali metal hydroxide are added to a mother liquor, to thereby cause a catalyst component in the form of oxalate salt to precipitate, and the catalyst component is dissolved in acetic acid serving as a solvent, followed by oxidation for recovery of the catalyst component (see Patent Document 2). There have also been known methods for recovering a catalyst component from a mother liquor by use of an anion exchange resin (see Patent Documents 3 to 11), including a method in which a bromide-ion-type anion exchange resin is exposed to a mother liquor for adsorption of cobalt ions and manganese ions on the resin, hydrous acetic acid having a water content of 2 mass % and water are caused to pass through the resin, to thereby recover cobalt ions and manganese ions through elution, a lower-aliphatic-monocarboxylate-ion-type weakly basic anion exchange resin is exposed to an eluate obtained through the aforementioned adsorption for adsorption of bromide ions and nickel ions on the resin, and hydrous acetic acid having a water content of 2 mass % and water are caused to pass through the resin, to thereby recover bromide ions and nickel ions through elution (see Patent Document 3); a method in which the cobalt concentration and the bromine/cobalt ratio of a mother liquor are respectively regulated so as to fall within specific ranges, followed by adsorption of cobalt and bromine on a strongly basic anion exchange resin, and cobalt and bromine are eluted from the strongly basic anion exchange resin with hydrous acetic acid having a water content of 10 mass % or more, to thereby recover a cobalt catalyst (see Patent Document 4); a method in which cobalt ions, manganese ions, and bromide ions are caused to be adsorbed together on an anion exchange resin containing a pyridine ring serving as an ion exchange group, and these ions are recovered through elution by a known technique (see Patent Document 5); and a method in which a catalyst component is recovered from a mother liquor by use of an anion-exchange-type chelate resin (see Patent Document 7).    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. S48-66090    Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. H02-203939    Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. S53-104590    Patent Document 4: Japanese Patent Application Laid-Open (kokai) No. S53-133574    Patent Document 5: Japanese Patent Application Laid-Open (kokai) No. S53-102290    Patent Document 6: Japanese Patent Application Laid-Open (kokai) No. H10-15390    Patent Document 7: Japanese Patent Application Laid-Open (kokai) No. H11-152246    Patent Document 8: Japanese Patent Application Laid-Open (kokai) No. 2002-12573    Patent Document 9: Specification of U.S. Pat. No. 4,162,991    Patent Document 10: Specification of U.S. Pat. No. 4,238,294    Patent Document 11: Japanese Kohyo Patent Publication No. 2003-507160